A pickoff mechanism is used in flat mail sorting machines to remove letters or the like one piece at a time from a stack of mail held edgewise against the pickoff mechanism. One such mechanism is shown in commonly-assigned U.S. patent application Ser. No. 12/186,122 filed Aug. 5, 2008, the contents of which are incorporated by reference herein.
Known pickoff mechanisms comprise a set of rubber belts side by side wound over a drive roller and a follower or idler roller. The belts engage the endmost mail piece of the stack and rely on friction to pull it sideways off of the stack and into the entry nip of the pinch belt conveyor. Friction is created by the pressure of the mail stack as it advances into contact with the pickoff belts. The stack is carried by a horizontal belt conveyor, and its remote end is supported by a paddle movably mounted on a frame of the feeder. The paddle and belt are synchronized to move the stack forward in increments. This is controlled by a letter present sensor, for example, an optical displacement sensor or a mechanical proximity switch using a spring arm which indicates to the feeder controller that the end of the stack is in engagement with the outer face of the pickoff belts.
The follower roller is adjusted (moved away from the drive roller) to create tension in the pickoff belts. Existing pick off belts tensioning devices use linear springs, an asymmetrical lever, and a cam to set tension. In these prior systems an Allen key is required to change the belt tension, and often a screw driver is used as a lever to increase/decrease tension if friction in the system becomes so great that the spring does not generate sufficient belt tension. Maintaining sufficient belt tension directly contributes to throughput of the pickoff mechanism, and the existing system proved insufficient for use in the DBCS 7 model postal sorting machine.